Production of wood pulp



Patented Aug. 8, 1933 PATENT OFFICE PRODUCTION or WOOD PULP Lemuel B. Decker, Kenogami, Quebec, Canada No Drawing. Application February 13, 1932 Serial No. 592,837

27 Claims.

The present invention relates to the production of wood pulp suitable for the manufacture of paper and the like, particularly newsprint.

This application is a continuation in part of my United States application Serial No. 440,111 filed March 29, 1930, entitled Process and apparatus for manufacturing wood pulp.

Up to the time of my present invention, it has been a common practice, in the manufacture of newsprint and similar papers, to employ a wood pulp consisting of a mixture of what is known as sulphite and groundwood, usually in the proportion of sulphite and 75% groundwood. The groundwood pulp is manufactured by a me- 15 chanical process of grinding wood blocks, in the form of logs or billets, ordinarily on revolving grind stones. This pulp constitutes the cheap furnish as no chemical treatment is necessary and a large yield, usually about 90% of the weight of the original wood, is obtainable. The sulphite pulp, produced by reducing wood blocks to small particles, known in the art as chips, and in subjecting the chips to a severe chemical cooking treatment during which substantial disintegration is effected, constitutes the high cost furnish, due largely to the expense of the chemical operation and the relatively low yield, which is generally from 40 to 50 '70 of the weight of the original wood. The sulphite pulp was used as it supplied desirable qualities, such as improved strength, in which the lower cost mechanical groundwood is deficient.

I have discovered a process by which a groundwood pulp, when subjected to a preliminary treatment under certain conditions, as will be hereinafter more fully described, can be successfully employed in substitution for the sulphite furnish in the manufacture of paper and the like. This special groundwood can be produced at a substantial economy, as compared with sulphite, due, largely, to the lower expense of the chemical treatment and the greatly increased yield. An important feature of the present invention is the production of a pulp of relatively low cost capable of substitution for all or a part of the sulphite pulp heretofore employed in the manufacture of newsprint and analogous products.

A further object of the invention is the provision of a pulp suitable to replace sulphite which will effect a substantial increase in yield production and, consequently, in preservation of timber resources.

Another feature of the invention resides in the production of a comparatively low cost pulp embodying characteristics essential to the manufacture of high grade paper and which will, when combined with mechanical. groundwood, enable (30 production of good quality newsprint.

Other objects and advantages of the invention will become apparent as the description progrosses.

In carrying out my invention, a vessel, some- 5 what similar to what is known in the art as a digester, is charged with wood blocks, that is, wood in relatively large pieces such as barked logs or billets. I then close the vessel and introduce therein a chemical liquor, in the present instance a sulphite solution containing lime or other suitable basic material, characterized by its high free sulphur dioxide content.

Upon completion of the filling operation, the contents of the vessel are subjected to heat and pressure. The heat, pressure and duration 01' treatment are regulated so as to eifectively impregnate and soften the blocks without, however, causing substantial disintegration thereof.

It is also quite important to remove the contents of the vessel in a particular manner, as will be apparent as the'description progresses, to obviate formation of objectionable residue on the blocks and to enable efficient grinding thereof.

Referring more specifically to a method of conducting the treatment, a removable cover, mounted to normally close a filling opening in the top of the vessel, is disconnected and the vessel charged with the wood blocks in the form of logs. The cover is thereafter replaced and the chem-- ical liquor, that is, a sulphite solution containing lime or other equivalent basic material and having a high free sulphur dioxide. content, as for instance, one per cent (1%) combined and five per cent (5%) free sulphur dioxide in solution, is introduced into the vessel through the bottom to completely fill the same.

Steam, under pressure, is injected through a conduit connecting with the bottom of the vessel, in order to attain the proper operating temperature and pressure. In the present example,

I have used a pressure of about seventy lbs. per square inch. The steam is admitted for a sufiicient period of time, usually about two hours, to attain a working temperature between 90 and C.

Although the pressure may be varied from that herein indicated, I consider it advisable in 110 any case to conduct the treatment below the boiling point of the liquor.

During the treating operation liquor is introduced, through a conduit connecting with the bottom of the vessel, to effect suitable circulation and preserve an approximately uniform liquor strength therein. As the vessel is maintained in a filled condition during the operation of the process, the excess, produced by the liquor injection and steam condensation, is relieved therefrom through a conduit connected with the top of the vessel.

When the desired operating temperature is attained, I find it desirable to cut off the main steam supply direct to the vessel and to maintain a uniform liquor temperature by regulating the temperature of the liquor supplied to the vessel. Thus, when the liquor to be injected into the vessel is of a lower temperature than that of the treating liquor therein, the temperature thereof is raised by injecting a suitable supply of steam into the conduit through which the liquor is injected. On the other hand, when the supplied liquor is of a temperature higher than that of the treating liquor, it may be correspondingly cooled.

I find that operation of the treatment, with a pressure of about seventy lbs. per square inch and a temperature between 90 and 116 (3., should be maintained for a period of about twelve hours when the wood employed is in fairly dry condition. The duration of treatment, however, can be readily determined by those skilled in the art in accordance with variation of conditions, as for instance, the species, maturity and moisture content of the wood.

Upon completion of the impregnation treatment, the respective conduits, through which liquor is injected and relieved, are closed. The liquor is removed from the vessel through a discharge outlet at the bottomthereof. Upon removal of the liquor, a sulphurous or sulphur d oxide gas accumulates in the vessel. This gas is withdrawn by connecting a vacuum line with the vessel so as to extract the gas therefrom and from the blocks remaining therein.

As a result of the treatment described in the foregoing, efiicient and adequate penetration and softening of the blocks is accomplished, although practically no appreciable disintegration of lignin or discoloration is efiected. While the softening action has been sufficient to reduce the amount of power consumed in grinding he treated blocks they are not softened to the extent of creating grinder operating difliculties.

The pulp obtained by the exercise of the present process is characterized by a favorable white colour, efficient bonding properties and an average fiber length considerably greater than that obtained in groundwood pulp. It is eminently suitable as a substitute for sulphite pulp as paper produced therewith is efficient in strength, opacity and other qualities and is favorably comparable with that produced by the use of sulphite or equivalent chemical pulps.

Inasmuch as the chemical treatment employed in the practice of my process is less severe and, in consequence thereof entails a smaller consumption of chemicals and steam, and the greatly increased yield, approximately to of the original wood, the pulp produced thereby is substantially cheaper than sulphite. In addition to the accepted pulp from the grinder, the screenings are in such soft and clean condition that they may be economically recovered as good pulp by a simple mechanical refining. Furthermore, the recovered product is in very clean condition as foreign matter, such as, pieces of bark, decayed wood and knots are separated and settled in the bottom of the vessel.

Having thus described my invention, I claim:

1. A process of treating wood for the production of pulp which consists in the successive steps of immersing wood in log form in a sulphite liquor, and treating the wood in the liquor at an approximately uniform temperature for a period of time sufficient to effectively impregnate the wood.

2. A process of treating wood for the production of pulp which consists in the successive steps of immersing wood in log form in a sulphite liquor, and treating the wood in the liquor while applying heat to maintain a relatively uniform temperature during the major duration of the treatment, and continuing the treatment for a period of time suflicient to effectively impregnate the wood.

3. A process of producing pulp which consists in the successive steps of immersing wood in log form in a sulphite liquor, treating the wood in the liquor while applying heat regulated to maintain an approximately unifom temperature during the major duration of the treatment, continuing the treatment for a period of time sufficient to effectively impregnate the wood, and grinding the wood in the ordinary manner.

'4. A process of treating wood for the production of pulp which consists in t'eating wood in log form in a sulphite liquor heated and maintained during the treatment at an approximately uniform temperature below boiling, and continuing the treatment for a period of time sufficient to impregnate and soften the blocks.

5. A process of treating wood for the production of pulp which consists in treating wood in log form in a sulphite solution containing a base and an excess of uncombined sulphur dioxide, under regulated conditions of temperature, pressure and duration of treatment to effectively impregnate the wood without causing substantial disintegration.

6. A process of producing pulp which consists in the successive steps of treating wood blocks in a sulphite solution in a closed vessel at an approximately uniform temperature below the boiling point under super-atmospheric pressure and for a period of time regulated to cause impregnation and softening of the wood, and disintegrating the treated blocks on grinding apparatus.

'7. A process of producing pulp which consists in treating wood blocks in a sulphite solution in a closed vessel at a temperature and pressure maintained substantially uniform during the major' duration of the treatment, continuing the treatment for a period of time regulated to effectively impregnate and soften the blocks without decomposition, and disintegrating the blocks on ordinary grinding apparatus.

8. In a process of treating wood for the manufacture of pulp, the steps which consist in treating wood, in log form, in a sulphite solution containing an excess of free sulphur dioxide at a temperature not over 110 C.

10. A process of treating wood for the manufacture of pulp which consists in the successive steps of immersing wood blocks in a treating liquor, subjecting the blocks to treatment in the liquor under regulated conditions of temperature,

pressure and length of treating time until the.

blocks are effectively penetrated and softened without decomposition or discoloration, and maintain a condition suitable for grinding to produce a long fibered pulp.

11. A process of producing pulp which consists in immersing wood in log form in a treating liquor, subjecting the wood to treatment in the liquor at an approximately uniform temperature and under super-atmospheric pressure, continuing the treatment until the wood is effectively penetrated and softened but not until the lignin is decomposed, and disintegrating the wood on ordinary grinding apparatus.

12. A process of producing pulp which consists in immersing wood in log form in a sulphite solution, subjecting the wood to treatment in the liquor at a super-atmospheric pressure and a temperature maintained substantially uniform, continuing the treatment for a period of time sufficient to impregnate and soften the wood without decomposition of the lignin, and disintegrating the wood on ordinary grinding apparatus.

13. A process of producing pulp which consists in treating wood blocks in a sulphite solution at a temperature between 90 and 110 C., and grinding the blocks.

14. A process of producing pulp which consists in subjecting wood blocks to treatment in a sulphite solution at a temperature between 90 and 110 C. for a period of time suitable to impregnate and soften the blocks, and grinding the blocks.

15. A process of producing wood pulp which consists in charging a vessel with wood blocks, introducing a sulphite liquor into the vessel, treating the blocks in the liquor at an approximately uniform temperature for a period of time suitable to impregnate the blocks, and grinding the blocks.

16. A process of producing wood pulp which consists in charging a vessel with wood blocks, in troducing a sulphite liquor into the vessel, treating the blocks in the liquor at an approximately uniform temperature between 90 and 110 C. for a period of time suitable to impregnate the blocks, and grinding the blocks.

17. A process of producing wood pulp which consists in charging a vessel with wood blocks, introducing a sulphite liquor into the vessel, treating the blocks in the liquor at a super-atmospheric pressure and at an approximately uniform temperature between 90 and 110 C. for a period of time suitable to impregnate the blocks, and grinding the blocks.

18. The process of treating wood for the manufacture of pulp which consists in the successive steps of subjecting the wood to treatment in a treating liquor in a closed vessel, removing the liquor from the vessel, and creating a vacuum in the vessel before the removal of the wood.

19. The process of treating wood blocks for the manufacture of pulp which consists in the successive steps of subjecting the wood to heat treatment in a sulphite solution in a closed vessel, removing the liquor from the vessel, and creating a vacuum in the vessel before removal of the wood.

20. The process of treating wood blocks for the manufacture of pulp which consists in subjecting the wood to heat treatment in a sulphite solution in a closed vessel under regulated conditions of temperature, pressure and duration of treatment to impregnate and soften the wood, removing the liquor from the vessel, and creating a vacuum in the vessel before removal of the wood.

21. The process of treating wood blocks for the production of pulp which consists in charging a vessel with wood blocks, introducing a sulphite liquor into the vessel, treating the blocks in the liquor at an approximately uniform temperature and for a period of time suitable to impregnate and soften the wood, removing the liquor from the vessel, and creating a vacuum in the vessel before removal of the wood.

22. As a new article of manufacture, a groundwood pulp suitable for the manufacture of paper produced by subjecting wood in log form to a preliminary treatment in a sulphite solution at an approximately uniform temperature for a period of time suitable to impregnate and soften the wood comprising a-relatively long fibered pulp containing the essential paper making characteristics of sulphite pulp.

23. A process of producing wood pulp for the manufacture of paper consisting in grinding wood blocks previously impregnated with an aqueous solution of free and combined sulphur dioxide by immersion under pressure in such a solution maintained at a temperature of between 90 C. and 110 C. during substantially the whole period of immersion. I

24. Wood pulp for the manufacture of paper prepared by grinding wood blocks previously impregnated with an aqueous solution of free and combined sulphur dioxide by immersion under pressure in such a solution maintained at a temperature of between 90 C. and 110 C. during substantially the whole period of immersion.

25. Paper manufactured wholly or partly from wood pulp prepared by grinding wood blocks previously impregnated with an aqueous solution of free and combined sulphur dioxide by immersion under pressure in such a solution maintained at a temperature of between 90 C. and 110 C. during substantially the whole period of immersion.

26. Wood pulp having substantially the composition of pulp prepared by the ordinary groundwood process and being suitable for use as a substitute for standard sulphite pulp in the man- 

